Commutator bar



Mwah 2f C J. WERNER COMMUTATOR BAR Filed April l0, 1946 INVENTOR CALL wmf Vf. wfg/yf@ Patented Mar. 2, 1948 COMIVIUTATOR BAR Calvin J. Werner, Dayton, Ghio, assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application April 10, 1946, Serial No. 660,886

3 Claims. 1

This invention relates to improvements in cornmutator bars and the method of producing them.

It is among the objects of the present invention to provide a commutator bar of composite construction, the part thereof which is gripped to hold the bar in assembled position in the commutator being made of any suitable strong and rigid material such as steel and the portion thereof adapted to be engaged by a brush and connected to a field winding being made oi a material having a substantially high electrical conductivity such as copper.

A further object of the present invention is to provide a composite commutator bar comprising a steel core with a copper covering attached thereto in such a manner that the copper covering will not separate from the steel core due to heat, centrifugal force or any other cause during the operation of the commutator on an electric machine. This may be accomplished by bonding the copper covering to the steel core in any suitable manner, as for instance by welding.

A still further object of the present invention is to produce a commutator bar as defined in the two paragraphs aforegoing in the simplest and most economical manner as regards both time and expense. This object is accomplished by forming a copper clad rod or wire comprising asteel rod or wire having a coating of copper bonded thereto, into a substantially flattened strip of desired cross sectional shape, then severing sections from this strip to provide the ccmmutator bars.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the invention is clearly shown.

In the drawings:

Fig. 1 is a perspective View of the commutator bar.

Fig. 2 is a. cross sectional View of an assembled commutator equipped with the present invention.

Fig. 3 is a fragmentary, longitudinal section of a, commutator (at reduced scale) equipped with the present invention.

Fig. 4 is a cross sectional view of a copper clad rod.

Fig. 51s a cross section oi the strip, formed from the copper clad rod of Fig. 4.

Fig. 6 is a plan view of a portion of the formed strip, the dot and dash lines indicating the outlines of the commutator bar severed therefrom.

Fig. 7 is a cross sectional view of another copper clad bar or wire.

2 Fig. 8 is a cross sectional View oi the strip formed from the bar or wire by the first operation.

Fig. 9 is a cross sectional View of the strip after the second operation.

Fig. 10 is a plan view of part of the strip, the dot and dash lines indicating the lines of severance to form commutator bars.

Referring to the drawings, the commutator bar 20 of the present invention is shown in perspective in Fig. l. Like the ordinary commutator bar commonly used in electric machines such as mctors and generators, the bar of the present invention is keystone-shaped in cross section. When viewed at its hat side, the bar has a rectangularly shaped body 2l from the thinner, longitudinal edge of which there extends a Wedge shaped tang 22. To hold the commutator bar in proper assembled position relatively to the other bars that make up the complete commutator, this tank portion 22 of each bar is rigidly clamped between the members 3i! and 3i as shown in Fig. 3 and as will detailedly be described hereinaiter.

Unlike the ordinary commutator bar commonly used and generally made completely of copper, a soft and very ductile metal but of high electrical conductivity, the bar of the present invention is a composite article having a core of rigid and comparatively tough metal such as steel, covered with a copper coating 24 to provide the electrical conductivity necessity for a device of this kind.

If, during the assembling of a commutator cornprising the ordinary, all copper bars, the clamping elements 3l] and 3| are drawn together excessively tight, the soft and ductile tank portions of the bars or at least some of the bars in the assembly will be bent and damage will result. If on the other hand the clamping elements it and 3! are not drawn together sufficiently tight, then the bars in the assembly will loosen during operation and a faulty and inoperative commutatcr will result. When, however, bars according to the present invention are used, the clamping elements 33 and 3i may be drawn up exceedingly tight without such damaging result, for the tangs of the present bars have a core of rigid and tough steel 23, not easily bent and capable of taking heavy clamping pressure. This assures the assembled commutator against loosening up and thus becoming inoperative.

To serve its purpose in an electric motor or generator, it is not necessary that the commutator consist of bars completely made of a metal having high electrical conductivity. It is sufcient thatl the surface of the bar, engaged by the brush of the motor or generator and connected to the field winding of the armature be of a metal of good electrical conductivity. The other portion of the bar need not be electrically conductive.

The cross sectional View Fig. 2 shows a commutator assembly comprising bars of the present invention. The core.y 2% is of rigid and tough metal, preferably of steel. This includes also the wedge-shaped tang 22 as shown in Fig. 3. The

copper coating 24 is comparatively thick as atV 25, which is the wider, longitudinal edge, of the bar, adapted to be engaged by the brushes ofthe electric machine of which the commutator forms a part. machine may be attached to this thicker edge of the bar in any suitable manner.

The two converging, substantially flat si'des of the bar core 23 are coated with a comparatively thin layer of copper designated in the Fig. 2 by the numeral. 26. This thin copper coating 28 on the opposite sides of the bar 20 is not necessary for the proper functioning of a commutator, but is merely incidental to. the vmethod. and means used for producing the bar as. illustrated. Thel comparatively thick copper section 25 on the wider,` longitudinal. edge of the keystone-shaped bar is, however, essential.

Figs. 4, 5 and 6 are provided to disclose one method of producing commutator bars according` to the presentA invention. In Fig.. 4 a cross section of a.v copperV clad rod or' Wire is illustrated. Here the steel rod or wire is designated by the numeral 23, andthe copper coating; or covering, bonded to the wire is designated by the numeral H24'. This typev of. copper clad wire may be purchased on the open market. By any suitable process,` as for instance rolling, the copper clad wire is formed into a. substantially flattened stripy having a keystone-shaped cross; section asV shown in Fig. 5. Now the steel core |23Y of the wire shown in Figa has been formed sov that it is keystoneshaped as shown at 23v in Fig. 5. The copper annulusv 121i of Fig. 4', forming a coating on wire |23' has been deformed soY that only a thin coating 25, Fig. 5, covers the converging, flat surfaces of core 23, and at the wider, longitudinal edge of'thestripthe copper covering24 is comparatively thick as at 25 in Fig. 5. The copper coating is still bondedV to the steel core, `but during this forming process the copper has been deformed and caused to fiow whereby the substantially thick area is provided on the wide, longitudinal edge of the strip and a comparatively thin area covers the two, converging surfaces of the core.

In the next operation sections are severed, by punching or any other suitable process, from this formed strip to produce the commutator bars. As has previously been stated, the commutator bar comprises a rectangularly shaped body portion, (viewed from the at side) keystone-shaped in cross section, the thinner, longitudinal edge thereof having a wedge-shaped tang extending therefrom. Thus when sections are severed from the formed strip, as illustrated by the dot and dash lines of Fig. 6, the tang side of the bar is severed from thethinner edge ofthe strip while the rectangular body portion of' the bar is formed from the thicker portion ofthe strip so that the thick copper side 25 of the strip forms the wider, longitudinal edge of the completed bar.

After the bars are assembled in a commutator as shown in Fig. 2 the assembly is machined to eliminate therounded, crowned edges of the bars thereby providingan even, annular sur-race upon The armature winding of the electric which the brushes of the electric machine, with which the commutator is used, may smoothly ride. The dotted lines 25a shown in Fig. 2, illustrate the excess copper of the rounded crowned edges of the bars which is removed by machining after the commutator bars are assembled.

The Figs. 7, 8, 9 and 10 illustrate the steps of another, modified process of producing the coma tightening under others.

mutator bars of the present invention. Here the steel wire or rod 22S of Fig. 7 is covered with a copper coating 22d also bonded to the rod.

The first operation consists of deforming the copper clad wire of Fig. '7, by rolling or otherwise, into. a substantially flattened shape as shown in Fig. 8. This operation causes the two parallel sides of the iiattened strip core 23 to have only a thin coating 2S of copper while the copper at its two longitudinal edges is comparatively thick as at 25.

This flattened strip is again operated upon to deform it so that it has a cross sectional shape as illustrated by Fig. 9. After the operation the strip is thinnest at its longitudinal center, the edges thereof being substantially as wide as after the iirst operation. This second operation renders the copper covering portion 26 thinner and the copper edge portions 25 thicker than by the rst operation. New the cross sectional shape-oi the formed strip is in the shape of an hour glass with the thinnest portion at the. longitudinal center of the strip. Thus one-half of the section may be said to be keystone-shaped as well as the other half or at least one portion thereofto be keystone-shaped in cross section.

After the strip is formed to have -a cross sectional shape as ilustrated in Fig. 9, sections are severed from the strip as shown by the dot and dash lines oi Fig. 1G, to produce commutator bars of the desired shape and conformation. The tang portions of the bars are severed or struck from the central, thinner area of the strip while the main body portion of the bars comprises the thicker sides of the strip. This provides the substantially thick copper covering portion 25 on the wider, longitudinal edges of the commutator bars.

As in the case of the bar produced by the first described method, the bars oi this last disclosed method are machined, after assembly in a cominutator, to eliminate the arched and rounded surfaces of adjacent bars in order to provide 'a smooth, annular surface upon which brushes may ride.

From the aforegoing it may be seen that applicant has conceived and devised an improved commutator bar and the method of producing it. The bar is a distinct and novel improvement over the ordinary commutator bar now used in that structural dimculties are eliminated without in any way aiecting the electrical qualities or requisites of a standard commutator bar. The bar of the present invention is more rigid and stronger than the ordinary bar and thus eliminates breakdowns resulting from inherent weaknesses of the ordinary bar. It may readily be understood that when all copper bars are clamped between steel jaws on a steel shaft, the differences of' expansion oi the copper and steel under varying temperature conditions will cause a loosening up under certain circumstances and However, when the bar of the present invention is used, material in the clamped portion or tang of the bar is of substantially the same material or a rial having substantially the same coefficient of expansion and thus these undesirable and generally damaging, loosening and tightening effects are entirely eliminated. On the other hand the bar of the present invention is just as good and eflicient electrically as the ordinary bar.

While the embodiments of the present invention constitute preferred forms, it is to be understood that other forms might be provided, al1 coming within the scope of the claims which follows.

What is claimed is as follows:

1. A composite commutator bar, keystoneshaped in cross section and comprising a core of comparatively tough metal having converging sides, two longitudinal edges, one wider than the other and two end edges, and a metal covering secured to all surfaces of the core excepting the end edges, said covering having a greater electrical conductivity than the core and being substantially thin on the two converging sides of the core and comparatively thicker on the Wider, longitudinal edge of the core.

2. A composite commutator bar, keystoneshaped in cross section and comprising a steel core having converging sides, two longitudinal edges, one wider than the other and two end edges; and a copper coating on all surfaces of said core excepting the end edges, comparatively thin on the two converging side surfaces of the core and substantially thicker on the wider, 1ongltudinal edge of the core.

3. A composite commutator bar, keystoneshaped in cross section and comprising a core of stii metal having converging sides, longitudinal edges, one wider than the other and end edges; and a copper cover bonded to all surfaces of said core excepting the end edges, the copper cover being comparatively thin on the two converging side surfaces of the core and substantially thick on the wider, longitudinal edge of the core.

CALVIN J. WERNER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

